Almost everybody with narcolepsy type 1 carries one particular HLA type. So do perhaps one in six people who will never develop it. It is the strongest association of its kind in medicine and it is nearly useless as a test — which is the most important thing on this page.
Deep in the hypothalamus sits a small population of neurons that make a signalling molecule called hypocretin, also known as orexin. Their job is to hold the boundary between sleeping and waking. In narcolepsy type 1, most of those neurons are gone — commonly more than 90% of them — and the boundary stops holding.
What follows is not simply sleepiness. Fragments of sleep intrude into waking life: overwhelming daytime sleep attacks, dreaming at the moment of falling asleep or waking, an inability to move for a few seconds on waking, and cataplexy — a sudden loss of muscle tone triggered by laughter or surprise, in which the person stays fully conscious. Cataplexy is the feature that separates type 1 from type 2, and it is close to unique to this condition.
Nearly everybody with narcolepsy type 1 carries the HLA type DQB1*06:02. As a disease association it is the strongest known between an HLA type and any condition, and it is what first suggested that narcolepsy is autoimmune — that the hypocretin neurons are destroyed by the immune system rather than lost to something else.
And it is nearly useless for telling an individual anything. Somewhere between one in eight and one in four people in the general population carry the same HLA type, and the overwhelming majority of them will never develop narcolepsy, which affects fewer than one person in two thousand.
So the test runs in one direction only. Not carrying DQB1*06:02 makes narcolepsy type 1 unlikely and is used that way in clinics. Carrying it says almost nothing, because so does a large part of the population sitting around you.
This is the clearest example on this site of a distinction the entire catalogue depends on: an association can be real, enormous, and still tell an individual nothing. If you take one thing from this page, take that.
HLA types are not ordinary single-letter variants. They are determined by dedicated HLA typing, and while some consumer arrays report a marker that stands in for DQB1*06:02, a proxy is not the type itself and the accuracy differs by ancestry.
Narcolepsy is diagnosed in a sleep clinic — by history, by an overnight study followed by daytime nap testing, and where needed by measuring hypocretin in cerebrospinal fluid. Nothing in a genotype file diagnoses it or rules it out.
Most people with narcolepsy have no relative with it, and identical twins are frequently discordant — one has it, one does not. Something has to happen on top of the genetic background, and the evidence points to an immune trigger. The clearest instance came from Northern Europe after the 2009 H1N1 pandemic, where narcolepsy incidence rose in children and adolescents who had received one particular adjuvanted influenza vaccine, which is no longer in use. It remains the strongest evidence for the autoimmune model and it is not a general finding about vaccines.
Type 1 and type 2. Type 1 involves cataplexy and low hypocretin. Type 2 has the sleepiness without cataplexy and usually with normal hypocretin, a weaker HLA association, and a less well understood cause. Most of what is written about the genetics of narcolepsy is about type 1.
How it is diagnosed. An overnight polysomnogram followed by a multiple sleep latency test the next day, which measures how quickly somebody falls asleep across several naps and whether they enter dreaming sleep abnormally fast. Cerebrospinal fluid hypocretin-1 measurement is used where the picture is unclear and is the most specific test there is.
Beyond HLA. Variation in the T-cell receptor alpha locus and in other immune genes has been associated with narcolepsy in genome-wide studies. Each contributes a small amount next to HLA, and the pattern — immune gene after immune gene — is itself the argument for the autoimmune model.
Treatment. The lost neurons cannot be replaced, so treatment addresses the symptoms: wake-promoting drugs for the daytime sleepiness and, separately, treatment for cataplexy. Pitolisant is one of the wake-promoting options and the one with a genotype attached.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Narcolepsy comes down to these specific, well-studied positions — not a diagnosis.
Research-derived gene–drug associations only — not a prescription, dosing guide, or medical advice. Always follow your prescriber's guidance.
| Gene | Drug | What the research shows |
|---|---|---|
| CYP2D6 | Pitolisant | Pitolisant treats the excessive daytime sleepiness of narcolepsy by a different route from the stimulants: it blocks the histamine H3 receptor, which normally limits the brain’s own histamine release, so histamine signalling rises and wakefulness with it. CYP2D6 clears the drug, and a poor metaboliser reaches substantially higher concentrations on the same dose. The US prescribing information therefore caps the dose for CYP2D6 poor metabolisers at 17.8 mg once daily, against 35.6 mg for everybody else. This is a label requirement rather than a CPIC guideline: CPIC lists the pair at level A but has not published guidance for it. Dose decisions belong to the clinician managing the condition, not to a raw data file. (US prescribing information for WAKIX (pitolisant). CPIC lists the CYP2D6–pitolisant pair at level A but has not published a guideline for it.) |
Databases, guidelines and references
Almost certainly not. Between one in eight and one in four people carry it and narcolepsy affects fewer than one in two thousand. The association is real and it is one of the strongest in medicine, and it still says close to nothing about you as an individual. This is the clearest case on the site of the difference between those two statements.
Only approximately. HLA types are established by dedicated typing, and the markers a consumer array uses as a stand-in vary in accuracy between ancestries. It is an indication, not a result.
Not in a simple way. Most people who have it have no affected relative, and identical twins are frequently discordant. A close relative carries a raised risk relative to the general population, but the absolute risk stays low.
A sudden loss of muscle tone brought on by a strong emotion — usually laughter — during which the person remains fully awake and aware. It can be as small as a dropped jaw or as complete as a collapse. It is close to specific to narcolepsy type 1, which is why it separates type 1 from type 2.
Free to reuse. This page's text is original writing from freely-available research, licensed CC BY 4.0 — reuse it, including commercially, with attribution to MyGeneLog. It's general research-derived information, not medical advice or a diagnosis — see Terms of Use.